PROJECT SUMMARY Candidate: Juliet Emamaullee is an Assistant Professor of Clinical Surgery at the University of Southern California (USC) and an attending liver and kidney transplant surgeon at Keck Hospital and Children?s Hospital- Los Angeles. Dr. Emamaullee has been working with her proposed K08 mentor, Dr. Omid Akbari, and her co- mentor, Dr. Shahab Asgharzadeh, to learn about mass cytometry approaches to characterize immune responses and now has begun independent work to develop these techniques to analyze the process of rejection in liver transplant (LT) recipients. The project aims to provide her with additional skills and knowledge required to achieve her long-term goal of studying the immunologic mechanisms involved in development and progression of LT rejection in order to develop new diagnostic, preventative, and therapeutic approaches to improve post-LT outcomes. Career Development Plan: Dr. Emamaullee has strategically planned to gain the necessary training and mentoring that will be required for her successful transition to being an independent investigator through select coursework and a robust mentoring plan. She has also organized an advisory committee composed not only of leaders in the field but also those able to directly impact her career advancement. The immediate training objectives are focused on consolidating her expertise in: (1) advanced immunological techniques including mass cytometry; (2) bioinformatics and data analysis; and (3) immunological pathways of rejection in clinical LT. This will not only ensure that Dr. Emamaullee's research project progresses as planned but will also ensure her progress will be recognized through promotion and obtaining independent research funding. She has an impactful, unique research project that is sufficiently different from her mentor's research to avoid competition or overlap. Research Plan: The proposed study leverages the extensive resources available at USC to address an important public health issue, which makes it directly relevant to the NIH mission. Hepatocellular carcinoma is on pace to become the leading global indication for LT, and rejection continues to be an important cause of graft loss and failure post-transplant. The diagnosis of rejection is not correlative to changes in liver blood tests and thus requires an invasive biopsy. Recently, there have been significant advances in the sensitivity of techniques to characterize immune responses, even in small tissue samples. We hypothesize that a liver-focused immune panel can be developed using imaging mass cytometry (IMC) to deeply analyze intrahepatic immune infiltrates in human liver tissue. We also hypothesize that graft-infiltrating lymphocytes can be characterized using IMC to better understand which subpopulations mediate allograft rejection in LT. First, we will develop a Liver Immunology IMC Panel using tissue obtained from LT patients with chronic rejection. Furthermore, we will utilize this assay to characterize graft-infiltrating lymphocyte subpopulations in chronic rejection and compare to results obtain using tissue obtained from LT patients with acute rejection. Immune profiles in each phase of rejection will be quantified and mapped, as well as compared to clinical parameters. Lastly, we will study LT patients prospectively to determine if these rejection-associated lymphocytes can be tracked in the blood during and after episodes of rejection. This project represents the first application of IMC in solid organ transplantation and has the potential to expand our knowledge of alloimmunity in clinical LT, which could provide the basis for a noninvasive assay of rejection in LT patients.